The invention relates to a tubbing lining for a tunnel or shaft.
The technical foundation for constructing modern subsurface structures is frequently based on insights gained from mining. In addition to the penetration of mountains with tunnel structures known from practical applications in regions with a demanding topology, there is an increased need especially in densely populated regions to construct infrastructure projects below the built-up surface. A sometimes feasible open construction method is frequently accompanied by serious interference with the above-ground use during the construction phase, so that the closed underground excavation is here also preferred. All these approaches require the obtained hollow space to be lined with at least one static load-bearing interior lining. In addition to the safe absorption of loading from the layers of earth above, in particular dynamic stress and convergence characteristics, for example caused by settling of the surrounding soil and rock, place high demands on the inner shell to be constructed for tunnels and shafts.
As already known since the mid-19th century, tubular annular segments successively arranged in the longitudinal direction, which are sometimes composed from individual segments, for example individual tubbing segments, can be used for the supporting inner shell. The required components can then advantageously be prefabricated with a reliable process and with high dimensional stability and introduced with a continuous excavation speed. The individual segments may be fabricated, for example, from cast iron or from concrete, where in the cast iron variant is also used as a lost shell for subsequent lining with concrete at the construction site. The single-shell construction method is typically preferred which simultaneously satisfies visual and static demands, while simultaneously providing a seal against hydraulic pressure.
Modern tubbing segments are nowadays used in form of prefabricated concrete segments as fixed support structure following closed shield driving. To obtain a closed static load-bearing tubbing construction, the individual tubbing sections are assembled inside the bored tube to a continuous tubbing ring. To obtain a static and water-impermeable total effect, the internally closed tubbing rings are then coupled with one another.
This produces a predetermined rigid circumference of the inner shell which does not permit adaption to deformations and other convergences of the rock formation. However, such movements begin mostly after the tunnel tube is driven in, causing compression of the rock formation surrounding the tube. This process may run at different speeds and may have a duration of several months. This noticeably increases loading of the supporting elements, which is already statically measured ahead of time and necessitates correspondingly larger dimensions of the individual components. Making the tubbing construction more economical requires this additional loading of the individual tubbing rings to be prevented by changing their respective cross-section for redistributing the surrounding forces.
EP 1 762 698 A1 discloses a flexible element for elongated subsurface spaces. In this embodiment, the flexible element is integrated between two mutually separated concrete shells arranged in the circumferential direction of the tunnel tube. The applied forces are distributed into circumferential ring forces and transferred to the flexible element, which yields under the pressure applied by the rock through compression. This embodiment has a substantially honeycomb-like structure with cavities which are reduced in size during the compression. This element satisfies its intended flexible behavior quite well.
EP 2 042 686 B1 describes an improvement of the flexible element known from EP 1 762 698 A1. This flexible element can be changed even after installation between the concrete shells by creating an increased resistance through reinforcement of the existing cavities by inserting of additional cavities. This allows in practice a better adaptation to local conditions.
The aforedescribed solutions are particularly suited for in-situ use with subsurface compound linings composed of channel profiles or lattice supports in combination with an in-situ concrete shell. The flexible element is hereby employed between two flexible in-situ concrete shells and cast in concrete into the concrete shells on both sides through a connecting reinforcement. Although the use in tubbing construction is mentioned, no practically application can be inferred, because the conventional tubbing segments are moved to the installation site as prefabricated elements, which makes subsequent integration in the hardened concrete body impossible. Moreover, tubbing segments are used in practical applications in a time-sequential method, where an in-situ incorporation of a flexible element between two tubbing segments facing each other in the circumferential direction would lead to inaccuracies, thus preventing loadbearing connections between the tubbing segments impossible. In addition, the flexible element does not have a compact structure that could be seamlessly integrated in the production of modern tubbing segments.
EP 0 631 034 B1 also discloses a controllably compressible compression bearing for tubbing segments in a tubbing ring from an elastically deformable material. This compression bearing is arranged in the butt joint between two tubbing segments that are successively combined to a tubbing ring with their end faces in a circumferential direction. The structure of the flexible element visually resembles the conventional structure of a horizontal coring brick and is predominantly composed of mutually parallel lands which intersect and thus form a plurality of continuous rectangular cavities. The cavities extend in the installed state between the opposite end faces of the tubbing segments. The elastic yieldability is controlled by filling the cavities with a plastically deformable fill mass, wherein the individual cavities may be connected with each other by passageways, thus allowing excess fill mass displaced by the compression to drain. The tubbing segments and compression bearing are connected with an adhesive. The actual pressure inside the compression bearing can be read out by integrating a pressure gauge and, if needed, reduced by draining the fill mass.
In practice, elastic materials experience aging, which may result in undesirable properties during the entire service life of the tubbing structure. The use of pressure-controlled fill masses at each of the compression bearings arranged inside the entire elongated structure requires substantial maintenance work. A decrease in the elastic properties may cause unnoticed perforation of the individual lands forming the hollow chambers, for example towards the outside of the tubbing ring which cannot be visually inspected. This would allow unimpeded draining of the fill material, which could cause an uncontrolled change in the entire geometry of the tubbing lining. However, the use of elastic materials carries certain risks even without the use of the fill material, because displacement of the elastic components under a compressive load is difficult to control. For example, “sliding” of two tubbing segments parallel to the butt joint in the lower ring half of the tubbing ring due to shear loads may endanger the ring static in the upper ring half, because the circumferential connection between the tubbing segments and the elastic compression bearings is solely based on an adhesive joint.
Based on the state-of-the-art, it is therefore the object of the invention to provide a tubbing lining as a tubular inner shell of a tunnel or shaft, which allows controlled and limited permanent load-bearing deformability in the circumferential direction, wherein the novel aspects can be seamlessly integrated in the prefabrication and the rapid installation of modern tubbing segments.